Hematopoietic stem cells (HSCs) are an important target for the gene therapy of infectious diseases, genetic disorders, and cancer. In vivo genome editing of HSCs has major advantages over currently used approaches that involve the collection of HSCs from patients, their in vitro culture/transduction, and retransplantation into myelo-conditioned patients. We have developed a new in vivo approach for HSC transduction, which is based on the GCSF/AMD3100-mediated mobilization of HSCs from the bone marrow into the peripheral blood stream and the intravenous injection of an HSC-targeting, helper-dependent adenovirus vector (HD-Ad5/35). The central goal of this proposal is to increase the percentage of stably in vivo HD-Ad5/35 - transduced HSCs while avoiding potential genotoxicity. We plan to achieve this through i) optimization of HSC mobilization and in vivo HSC transduction, ii) optimization of transgene integration through stimulation of homologous recombination, and iii) incorporation into HD- Ad5/35 vectors of systems that allow for the in vivo selection or expansion of stably transduced cells. Based on these studies, we will generate and test HD-Ad5/35 vectors for in vivo gene therapy of b-thalassemia.